1. Field of the Invention
This invention relates to a fuel injection system for an engine, and more particularly to an improvement in control of the amount of fuel to be injected during accelerating operation of the engine.
2. Description of the Prior Art
Conventionally, whether or not the engine is accelerated has been detected by detecting change in opening degree of a throttle valve provided in the intake passage of the engine, or by detecting change in intake vacuum in the intake passage downstream of the throttle valve. It has been proposed to supply an increased amount of fuel to the engine during accelerating operation of the engine thus detected by increasing the width of individual regular injection pulses or outputting a plurality of extra injection pulses of the same width. See Japanese Unexamined Patent Publication 57(1982)-143135, for example.
By the way, due to the shape of the throttle valve which is a so-called butterfly valve, change in the amount of intake air for a given amount of displacement of the throttle valve varies with the opening degree of the throttle valve. That is, the smaller the opening degree of the throttle valve is (i.e., the lighter the load on the engine is the larger the change in the amount of intake air for a given amount of displacement of the throttle valve is.
Thus there has been proposed to increase detection sensitivity in detecting engine acceleration or to increase the fuel increasing rate during accelerating operation of the engine as the load on the engine is reduced. However these proposal are disadvantageous in that complicated structure is required. Particularly, in order to accomplish both the proposals together with each other, very complicated structure is required.